1. Field of the Invention
The present invention relates to an insulated wire. More particularly, the present invention relates to an insulated wire which is excellent in winding and inserting properties to processing and preferably used as a wire to be wound around a core of a motor.
2. Description of the Related Art
In these years, as a tendency for down-sizing and weight reduction of electric or electronic apparatuses has increased, a smaller and lighter motor with higher performances has been required. To satisfy such requirement, it is necessary to wind more turns of an insulated wire around the core of the motor. To this end, the insulated wire is forced to be jammed in a core slot. Therefore, an insulating coating of the insulated wire tends to be damaged during winding. If the insulating coating is damaged, layer failure or earth failure occurs so that electric characteristics of the motor tend to be deteriorated.
Hitherto, in the motor to be used in the above described application, there is usually used an insulated wire having an insulating coating with good mechanical strength which is formed by coating and baking a coating paint of polyamideimide having good mechanical strength on a conductor or other insulating coating which is already formed on the conductor. As the polyamideimide, a reaction product of diphenylmethane-4,4'-diisocyanate and trimellitic anhydride is generally used (cf. Japanese Patent Publication Nos. 19274/1969 and 27611/1970).
Today, a further down-sized and weight reduced motor with better performances is required. To satisfy this requirement, the number of turns of the insulated wire is further increased so that even the polyamideimide base insulating coating is sometimes damaged.
To decrease the damage of the insulating coating, it is studied to add an organic or inorganic lubricant to the coating paint so as to impart lubricity to the insulating coating, or to apply a lubricant such as a wax directly on the insulated wire. However, these methods do not prevent the damage of the insulating coating completely.
The further increase of the mechanical strength of the insulating coating may decrease the damage of the insulating coating. However, simple increase of the mechanical strength will make the coating more stiff and less flexible, so that the coating is easily cracked or peeled off when the insulated wire is bent, or the winding and inserting properties of the insulated wire is deteriorated.